The present invention relates in general to a circuit for encoding identification, serialization, or other information on circuit dice.
There is a need for providing identification and other types of information on circuit dice or chips. For example, it may be desireable or necessary in circuit parameter studies to monitor small shifts in the values of the various circuit parameters of a test die over time. In order to observe such shifts accurately, a particular test circuit die must be used for each measurement because the variation of the circuit parameters from die to die may be comparable to, or even larger than, the shifts that are to be monitored. Consequently, some means must be provided by which a particular circuit die can be identified. The use of visible or optically readable marks and codes is not generally suitable because the dice are encapsulated so that the marks or codes can not be seen. As a result, electrical identification of the dice is the only workable solution, especially for large volumes of parts processed in production, assembly and test facilities. The only other alternative would be to maintain part identification with physical means, such as part carriers or identification bins, however, this solution is unworkable with large numbers of parts and the risk of misclassification is unacceptably high.
In technologies in which there are inherently built-in programmable structures, such as programmable memories, it is a rather straight forward procedure to use these available structures for encoding the identification information into the circuits. However, with other types of circuits that do not include any programmable structures, extra undesirable or impossible fabrication steps are required to add them which could have an effect on the measured circuit parameters that would defeat the whole purpose of the parameter study. For example, the identification circuitry may require extra layers of material or the use of non-standard masks which may be incompatible with current wafer stepper lithographic techniques, and thus could not be utilized therewith.